Using a significant number of electron micrographs, the major and minor periodicities of coagulase and biothrombin induced fibrin will be analyzed and compared quantitatively, with the aid of a magnifying Gaertner micrometer slide comparator. With the aid of embedding techniques, the relation of the striations to the surface and the interior of the fibrin strands will be analyzed. The comparative action of plasmin and other proteolytic enzymes on coagulase-fibrin and biothrombin-fibrin will be explored, with respect to ultrastructure and monomeric components on SDS gel electrophoresis and/or urea starch gel electrophoresis.